This invention relates to data communication and more particularly to obtaining reliable synchronization between a transmitter and a receiver over a noisy communication channel.
Synchronous methods of data transfer are often preferred when serial communication media are used because these methods permit higher throughput capability than asynchronous techniques. For proper functioning of synchronous systems, synchronization between a receiver and a transmitter is essential. When a communication system operates in a noisy environment, receiver synchronization is often lost due to noise. In order to permit the receiver to acquire and maintain synchronization with the transmitter, a commonly employed scheme periodically transmits binary synchronizing words including predetermined or pseudo random bit patterns. The receiver uses these synchronizing words to verify synchronization and to re-synchronize, if necessary. If the communication channel is noisy, synchronizing words may become corrupted, e.g., the transmitted bit pattern may be randomly altered, causing the receiver to lose synchronization and may ultimately result in failure to re-achieve it.
When noise characteristics of a communication medium are bursty, it is desirable to employ an interleaved message structure and forward error correction coding in order to overcome corruption of information due to noise. Further, it is also desirable to overcome corruption of synchronizing words due to noise and still achieve both bit and message synchronization and be able to re-acquire synchronization of the receiver after it has been lost.
In order to provide bounding, which gives an indication of where one message ends and the next message begins, it is often necessary to include delineation bits or code as part of the header and/or trailer along with the message being sent. Such bounding information contributes to overhead of the system in that it uses a portion of the available bandwidth which may be more efficiently allocated to intelligence data transmission.
Accordingly, it is an object of the present invention to provide a method and apparatus for bit and/or message synchronization.
Another object is to obtain accurate bit and/or message synchronization in a noisy environment, even if message bits are corrupted.
Yet another object is to provide a method and apparatus which permits rapid resynchronization after a receiver has lost synchronization with a transmitter.